A series of directional shear tests on remolded frozen soil was carried out at 10°C by using a hollow cylinder apparatus to study failure criterion under a directional shear-stress path.Directional shear tests we...A series of directional shear tests on remolded frozen soil was carried out at 10°C by using a hollow cylinder apparatus to study failure criterion under a directional shear-stress path.Directional shear tests were conducted at five shear rates(10,20,30,40,and 50 kPa/min)and five intermediate principal stress coefficients(b=0,0.25,0.5,0.75,and 1),with the mean principal stress(p=4.5 MPa)kept constant.The results show that the torsional strength and the generalized strength both increase with the increase of the shear rates.According to the failure modes of frozen soil under different shear rates,the specimens present obvious plastic failure and shear band;and the torsional shear component dominates the failure modes of hollow cylindrical specimens.A shear rate of 30 kPa/min is chosen as the loading rate in the directional shear tests of frozen soil.The shape of the failure curve in theπplane is dependent on the directional anglesαof the major prin cipal stress.It is reasonable to use the strain-hardening curves to define the deviatoric stress value atγg=15%(generalized shear strain)as the failure criterion of frozen soil under a directional shear-stress path.展开更多
In this paper, we give necessary and sufficient conditions for absolute stability of several classes of direct control systems, and discuss the absolute stability of the first canonical form of control system. The cor...In this paper, we give necessary and sufficient conditions for absolute stability of several classes of direct control systems, and discuss the absolute stability of the first canonical form of control system. The corresponding results in references [3,5,6] and [7] are improved.展开更多
In this paper,we propose a new stopping criterion for Eckstein and Bertsekas’s generalized alternating direction method of multipliers.The stopping criterion is easy to verify,and the computational cost is much less ...In this paper,we propose a new stopping criterion for Eckstein and Bertsekas’s generalized alternating direction method of multipliers.The stopping criterion is easy to verify,and the computational cost is much less than the classical stopping criterion in the highly influential paper by Boyd et al.(Found Trends Mach Learn 3(1):1–122,2011).展开更多
To predict hot tearing susceptibility(HTS)during solidification and improve the quality of Al alloy castings,constitutive equations for AA6111 alloys were developed using a direct finite element(FE)method.A hot tearin...To predict hot tearing susceptibility(HTS)during solidification and improve the quality of Al alloy castings,constitutive equations for AA6111 alloys were developed using a direct finite element(FE)method.A hot tearing model was established for direct chill(DC)casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion.By applying this model to real manufacture processes,the effects of casting speed,bottom cooling,secondary cooling,and geometric variations on the HTS were revealed.The results show that the HTS of the billet increases as the speed and billet radius increase,while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases.This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation,which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.展开更多
For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous stud...For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions,as well as the water effects on compressive and tensile strengths.In this study,andesite was subjected to direct shear tests under five water saturation conditions,which were controlled by varying the wetting and drying time.The tests were conducted at alternating displacement rates under three vertical stresses.The results reveal that the shear strength decreases exponentially as water saturation increases,and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses.Based on the findings of the shear tests in this study and the compression and tension tests in previous studies,the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined.These results indicate that the brittleness index of the andesite,which is defined as the ratio of uniaxial compressive strength to tensile strength,is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.展开更多
A method of reliability analysis based on a direct strength calculation employing the von Mises stress failure criterion is presented here. The short term strain distributions of ship hull structural components are id...A method of reliability analysis based on a direct strength calculation employing the von Mises stress failure criterion is presented here. The short term strain distributions of ship hull structural components are identified through the statistical analysis of the wave-induced strain history and the long term distributions by the weighted summation of the short term strain distributions. The wave-induced long term strain distribution is combined with the still water strain. The extreme strain distribution of the response strain is obtained by statistical analysis of the combined strains. The limit state function of the reliability analysis is based on the von Mises stress failure criterion, including the related uncertainties due to the quality of the material and model uncertainty. The reliability index is calculated using FORM and sensitivity analysis of each variable that has effects on the reliability is also discussed.展开更多
直流受端系统受扰后,极易引起直流发生换相失败、直流闭锁等故障,使得直流受端系统的暂态电压稳定(transient voltage stability,TVS)问题尤为突出,量化评估直流受端系统暂态电压稳定性具有重要意义。由于直流系统复杂的暂态特性,使得...直流受端系统受扰后,极易引起直流发生换相失败、直流闭锁等故障,使得直流受端系统的暂态电压稳定(transient voltage stability,TVS)问题尤为突出,量化评估直流受端系统暂态电压稳定性具有重要意义。由于直流系统复杂的暂态特性,使得现有的暂态电压评估方法难以准确评估直流系统的暂态电压问题。为此,基于现有的多二元表判据和直流系统暂态恢复特性,提出了两阶段暂态电压评估方法。首先,分析了直流系统的暂态电压恢复特性和现有多二元表在直流系统中的应用局限。其次,基于不同稳定性水平赋予不同权重的思想,提出两阶段暂态电压评估方法,结合直流控制参数和故障严重程度等信息,实现对暂态电压稳定性的评估。最后,基于双直流馈入系统和修改后含直流的IEEE 3机9节点系统验证两阶段暂态电压评估方法对直流系统的适用性,结果表明所提方法可以实现对直流受端系统暂态电压稳定的准确评估。展开更多
基金supported by the National Natural Science Foundation of China(Nos.U1703244 and 41672310)the National Natural Science Foundation of China(No.41801038)+6 种基金the State Key Laboratory for Geo Mechanics and Deep Underground Engineering,the China University of Mining and Technology(SKLGDUEK1904)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA2003020102)the Major Program of Bureau of International Cooperation,the Chinese Academy of Sciences(131B62KYSB20170012)the National Key Research and Development Program(2017YFC0405101)the Research Project of the State Key Laboratory of Frozen Soils Engineering(Grant No.SKLFSE-ZY-16)the Science and Technology Major Project of Gansu Province(143GKDA007)the Science and Technology Planning Project of Gansu Province(No.18JR3RA376)
文摘A series of directional shear tests on remolded frozen soil was carried out at 10°C by using a hollow cylinder apparatus to study failure criterion under a directional shear-stress path.Directional shear tests were conducted at five shear rates(10,20,30,40,and 50 kPa/min)and five intermediate principal stress coefficients(b=0,0.25,0.5,0.75,and 1),with the mean principal stress(p=4.5 MPa)kept constant.The results show that the torsional strength and the generalized strength both increase with the increase of the shear rates.According to the failure modes of frozen soil under different shear rates,the specimens present obvious plastic failure and shear band;and the torsional shear component dominates the failure modes of hollow cylindrical specimens.A shear rate of 30 kPa/min is chosen as the loading rate in the directional shear tests of frozen soil.The shape of the failure curve in theπplane is dependent on the directional anglesαof the major prin cipal stress.It is reasonable to use the strain-hardening curves to define the deviatoric stress value atγg=15%(generalized shear strain)as the failure criterion of frozen soil under a directional shear-stress path.
文摘In this paper, we give necessary and sufficient conditions for absolute stability of several classes of direct control systems, and discuss the absolute stability of the first canonical form of control system. The corresponding results in references [3,5,6] and [7] are improved.
文摘In this paper,we propose a new stopping criterion for Eckstein and Bertsekas’s generalized alternating direction method of multipliers.The stopping criterion is easy to verify,and the computational cost is much less than the classical stopping criterion in the highly influential paper by Boyd et al.(Found Trends Mach Learn 3(1):1–122,2011).
文摘To predict hot tearing susceptibility(HTS)during solidification and improve the quality of Al alloy castings,constitutive equations for AA6111 alloys were developed using a direct finite element(FE)method.A hot tearing model was established for direct chill(DC)casting of industrial AA6111 alloys via coupling FE model and hot tearing criterion.By applying this model to real manufacture processes,the effects of casting speed,bottom cooling,secondary cooling,and geometric variations on the HTS were revealed.The results show that the HTS of the billet increases as the speed and billet radius increase,while it reduces as the interfacial heat transfer coefficient at the bottom or secondary water-cooling rate increases.This model shows the capabilities of incorporating maximum pore fraction in simulating hot tearing initiation,which will have a significant impact on optimizing casting conditions and chemistry for minimizing HTS and thus controlling the casting quality.
文摘For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions,as well as the water effects on compressive and tensile strengths.In this study,andesite was subjected to direct shear tests under five water saturation conditions,which were controlled by varying the wetting and drying time.The tests were conducted at alternating displacement rates under three vertical stresses.The results reveal that the shear strength decreases exponentially as water saturation increases,and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses.Based on the findings of the shear tests in this study and the compression and tension tests in previous studies,the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined.These results indicate that the brittleness index of the andesite,which is defined as the ratio of uniaxial compressive strength to tensile strength,is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.
文摘A method of reliability analysis based on a direct strength calculation employing the von Mises stress failure criterion is presented here. The short term strain distributions of ship hull structural components are identified through the statistical analysis of the wave-induced strain history and the long term distributions by the weighted summation of the short term strain distributions. The wave-induced long term strain distribution is combined with the still water strain. The extreme strain distribution of the response strain is obtained by statistical analysis of the combined strains. The limit state function of the reliability analysis is based on the von Mises stress failure criterion, including the related uncertainties due to the quality of the material and model uncertainty. The reliability index is calculated using FORM and sensitivity analysis of each variable that has effects on the reliability is also discussed.
文摘直流受端系统受扰后,极易引起直流发生换相失败、直流闭锁等故障,使得直流受端系统的暂态电压稳定(transient voltage stability,TVS)问题尤为突出,量化评估直流受端系统暂态电压稳定性具有重要意义。由于直流系统复杂的暂态特性,使得现有的暂态电压评估方法难以准确评估直流系统的暂态电压问题。为此,基于现有的多二元表判据和直流系统暂态恢复特性,提出了两阶段暂态电压评估方法。首先,分析了直流系统的暂态电压恢复特性和现有多二元表在直流系统中的应用局限。其次,基于不同稳定性水平赋予不同权重的思想,提出两阶段暂态电压评估方法,结合直流控制参数和故障严重程度等信息,实现对暂态电压稳定性的评估。最后,基于双直流馈入系统和修改后含直流的IEEE 3机9节点系统验证两阶段暂态电压评估方法对直流系统的适用性,结果表明所提方法可以实现对直流受端系统暂态电压稳定的准确评估。
